In one type of optical information system computer generated images are projected onto a screen for viewing by a large number of people simultaneously. An important aspect of such a system is to enable a user to enter information interactively into the system to modify images, or generate additional images during presentation.
In one successful arrangement, a user points a light generating device, such as a flashlight or laser pointer, at a projected image to provide auxiliary information for the system. In this regard, such a system generally includes a video information source, such as a computer, and a display projection arrangement, such as an overhead projector, for projecting images of the video information onto a viewing surface. An image processing arrangement detects and processes the displayed image reflecting from the viewing surface. Such a system detects the high intensity light images produced by the hand-held light generating device, and discriminates them from background ambient light as well as the light produced by the video information source. In this manner, light signals from the hand-held light generating device can be detected on the viewing surface, and then used by the system for modifying subsequently the projected video information. Such an optical auxiliary input system is described in greater detail in the above-mentioned U.S. patent application Ser. No. 07/433,029.
While such an optical system and method of using it has proven highly satisfactory, such a system must be calibrated to assure the accurate communication of the user generated high intensity light information. Such calibration includes using a calibration arrangement to align properly an optical sensing device associated with the image processing arrangement relative to the viewing surface and the projected images. Such a calibration arrangement and method of using it, are described in greater detail in the above-mentioned copending U.S. patent application Ser. No. 07/611,416.
While such a calibration arrangement and calibration method has proven highly satisfactory under low ambient lighting conditions, such as in a darkened room, it would be desirable to facilitate calibration of such an optical system under a wide variety of ambient lighting conditions, even bright ambient lighting conditions. Moreover, such a calibration technique should be able to be employed with many different types and kinds of optical systems generating images with substantially different luminance levels, as well as contrast levels between bright and dark images.
Such a calibration technique includes the proper alignment of the system, so that the viewing area of the system light sensing device is positioned properly to capture the entire computer generated projected image. Such alignment is desirable, because the viewing surface or screen of the system may be positioned at various distances and angular positions relative to the system light sensing device.
Also, the calibration of such a system entails sensitivity adjustments. Such adjustments are frequently necessary to accommodate for various projector light source intensities, different optical arrangements employed in conventional overhead projectors, and different optical characteristics exhibited by various liquid crystal display units employed in such systems. In this regard, calibration adjustments must be made to distinguish between the luminance levels of the various images reflecting from the viewing surface. Such adjustments however, are dependent upon several factors: the optical characteristics of the overhead projector including the power rating of projector lamps, the optical characteristics of the liquid crystal display unit employed, the distance the overhead projector is positioned from the viewing surface, and the intensity level of the user generated auxiliary images reflecting from the viewing surface.
Each of the above-mentioned factors directly affect the ability of the light sensing device to receive properly a reflected image, whether produced via the light generating pointing device or the projection display arrangement. In this regard, for example, if the overhead projector utilized in the projection display arrangement, is positioned a substantial distance from a viewing surface, the resulting image is large in size, but its overall luminance level is substantially reduced. Similarly, if an overhead projector employs a low intensity bulb, the projected image produced by the projector results in only a low luminance level.
Therefore, it would be highly desirable to have a new and improved calibration arrangement and method to calibrate the alignment, and improve the light sensitivity of an optical information system. Such an arrangement and method should enable a user to align conveniently the system optical sensing device to capture substantially the entire viewing area of a projected image. The arrangement and method should also enable the light sensitivity of the system to be adjusted so that it can be utilized with different types and kinds of liquid crystal display projection systems, employing different liquid crystal display panels and projection system.
Another form of light sensitivity calibration necessary for such an optical input information system, is a calibration adjustment to distinguish between ambient background light, light from the high intensity user controlled light generating device and the light produced from the video image reflecting from the viewing surface. In this regard, because of variations in ambient background lighting, as well as various different intensity levels of both the high intensity auxiliary control light image, and light produced by the projection system, it is, of course, desirable to distinguish properly the auxiliary light image on the viewing surface or screen, from the other light being reflected therefrom.
While the system has operated highly successful for many applications, it has been difficult, in some situations, to distinguish properly between the various light sources. For example, a light sensing device, such as a charge couple camera, must be positioned, not only in alignment to capture substantially the entire image reflecting from the viewing surface, but also it must be positioned in relatively close proximity to the viewing surface to produce a signal of sufficient potential to be processed for information extraction purposes.
Therefore, it would be highly desirable to have a new and improved calibration arrangement and method to calibrate the alignment and light sensitivity of an optical auxiliary input information system so that an adjustment can be made conveniently so the system produces a sufficient amount of light for information processing purposes.
Conventional charge couple cameras, by the nature of their sensitivity to different levels of light intensities, typically produce a "haystack" shaped waveform signal in response to sensing an image produced by a projection system, such as an overhead projector. The haystack signal is the resulting response developed because the scattered light source of the overhead projector typically emanates from a light bulb centrally disposed beneath the stage of the projector. Such a response thus, makes it difficult to accurately detect auxiliary light information reflecting at or near the boundaries of a reflected image.
Therefore, it would be highly desirable to have a new and improved calibration arrangement and method for discriminating accurately and reliably between various intensities of light reflecting from a viewing surface under a wide variety of conditions. Such arrangement and method should also discriminate between different beam intensities produced by an auxiliary input light generating device over a wide variety of distances.